Our studies are concerned with the following aspects of the replication of and transformation by Rous sacroma virus: (1) The nucleic acids of RSV - including the S70 RNA and its components (the S35 subunits, the S4 and the S5 species, the S7 RNA, the S5 RNA, the S4 t- RNA's, and the S4 DNA; 2) the characteristics of transcription by the virion-associated DNA polymerase including an analysis of the DNA product and of the primer RNA molecules; 3) inhibitors of the DNA polymerase - specifically, the drugs cytosine arabinoside triphosphate and isatin beta-thiosemicarbazone. 4) Virus specific DNA and RNA in normal and infected cells - an investigation of the virus-specific nucleotide sequences in the DNA of normal and transformed cells of various species, plus the presence of virus-specific RNA and of group- specific antigen in these cells.